Google Pushes Invalid HTML to the World
So, Google started a Google Plus social network. Along with it is a Google Plus button, it looks like this:

To add Google Plus button, you get the code at the official Google site at http://www.google.com/webmasters/+1/button/ .

Part of the code is this:
<g:plusone annotation="inline"></g:plusone>
Invalid HTML!
isn't Google supposed to be this ethical company who promotes good coding practices and HTML5 for a better world?
addendum: This page used to also claim Twitter and Facebook using HTML5 Custom Data Attribute as invalid. That is incorrect. Thanks to ArgV for correction.